import java.util.*;
public class trianglearea{
    public double firstEdge;
    public double secondEdge;
    public double thirdEdge;
    public double p;
    public double s;
    public double f;
    public double x;

    public void squaring(){
        System.out.println( "三角形的面积为") ;
    }
    public static void main(String[] args) {
        trianglearea t = new trianglearea();
        t.firstEdge=30;
        t.secondEdge=40;
        t.thirdEdge=50;
        t.p=(t.firstEdge+t.secondEdge+t.thirdEdge)/2;
        t.s=(t.p*(t.p-t.firstEdge)*(t.p-t.secondEdge)*(t.p-t.thirdEdge));
        if(t.s>0){
            t.x=t.s;
        }
        else{
        t.x=-t.s;
    }
       
        t.f=Math.sqrt(t.x);
        
        
        t.squaring() ;
        System.out.println( t.f) ;
        
        
    }
}